slkern/drives.c

/* NEW CODE implementing a simple system like "drive letters" but longer names,
 * Copyright (C) 2024 Zak Fenton
 * NO WARRANTY USE AT YOUR OWN RISK etc. under terms of UNLICENSE or MIT license
 */
#include "types.h"
#include "param.h"
#include "memlayout.h"
#include "sched.h"
#include "riscv.h"
#include "proc.h"
#include "drives.h"
#include "defs.h"
#include "fs.h"
#include "kprintf.h"

#ifndef NULL
#define NULL ((void*)0ULL)
#endif

char* strcat(char*, const char*);
void* memcpy(void*, void*, long);


struct drives* drives_alloc() {
  int i;
  if (sizeof(struct drives) >= PGSIZE) {
    panic("drives structure too large to fit in a page");
  }
  struct drives* result = kalloc();
  if (result == NULL) {
    panic("failed to allocate drives structure");
  }
  initlock(&(result->lock), "drives");
  for (i = 0; i < DRIVES_MAX; i++) {
    result->entries[i].handler = DRIVES_HANDLER_NONE;
  }
  return result;
}

/* Returns the length of the drive name in the given string, allowing for
 * strings with more path information to be used in lookup (rather than copying
 * just the drive name to a new string!).
 */
static int drives_namelen(const char* n) {
  int i = 0;
  if (n == NULL) {
    return -1;
  }
  while (*n != 0 && *n != ':') {
    if (i >= DRIVES_NAMEMAX || *n == '/' || *n == '\\') {
      return -1;
    }
    n++;
    i++;
  }
  return i;
}

/* Like drives_namelen but checks that a drive name ending in ':' is actually
 * present (returning -1 otherwise).
 */
static int drives_namelencheck(const char* n) {
  int i = 0;
  if (n == (void*)0ULL) {
    return -1;
  }
  while (*n != 0) {
    if (*n == ':') {
      return i;
    }
    if (i >= DRIVES_NAMEMAX || *n == '/' || *n == '\\') {
      return -1;
    }
    n++;
    i++;
  }
  return -1;
}

/* Returns 1 if the name matches the given drive number or 0 otherwise. */
static int drives_namesmatch(struct drives* drives, int driveid, const char* name, int namelen) {
  int i;
  for (i = 0; i < namelen; i++) {
    if (drives->entries[driveid].name[i] != name[i]) {
      return 0; // Not a match, character differs
    }
  }
  if (i == DRIVES_NAMEMAX || drives->entries[driveid].name[i] == 0) {
    return 1; // Is a match, we checked until the end
  } else {
    return 0; // Not a match, drive name has more characters
  }
}

/* Scans the drives structure for a matching drive. Can be run without locking,
 * then the structure can be locked once a candidate is found.
 */
static int drives_find(struct drives* drives, int startingat, const char* name, int namelen) {
  int i;
  for (i = startingat; i < DRIVES_MAX; i++) {
    if (drives_namesmatch(drives, i, name, namelen) && drives->entries[i].handler != DRIVES_HANDLER_NONE) {
      return i;
    }
  }
  return -1; // Not found.
}

int drives_setup(struct drives* drives, int handlertype, void* handlerdata, const char* name) {
  acquire(&(drives->lock));
  
  int nlen = drives_namelen(name);
  int idx = drives_find(drives, 0, name, nlen);
  if (idx >= 0) { // Already exists
    release(&(drives->lock));
    return -1;
  }
  
  for (idx = 0; idx < DRIVES_MAX; idx++) {
    if (drives->entries[idx].handler == DRIVES_HANDLER_NONE) {
      drives->entries[idx].nusers = 0;
      drives->entries[idx].handler = handlertype;
      drives->entries[idx].handlerdata = handlerdata;
      int namei;
      for (namei = 0; namei < nlen; namei++) {
        drives->entries[idx].name[namei] = name[namei];
      }
      for (; namei < DRIVES_NAMEMAX; namei++) {
        drives->entries[idx].name[namei] = 0;
      }
      release(&(drives->lock));
      return idx;
    }
  }
  // No free slots
  release(&(drives->lock));
  return -1;
}

int drives_open(struct drives* drives, const char* name, int* handlertype, void** handlerdata) {
  acquire(&(drives->lock));
  int nlen = drives_namelen(name);
  int idx = drives_find(drives, 0, name, nlen);
  
  if (idx < 0) {
    release(&(drives->lock));
    return idx;
  }
  
  drives->entries[idx].nusers++;
  
  release(&(drives->lock));
  
  return idx;
}

int drives_opensimple(struct drives* drives, int driven) {
  if (drives == NULL || driven < 0 || driven > DRIVES_MAX) {
    return -1; // Return -1 to indicate error
  }
  acquire(&(drives->lock));
  
  drives->entries[driven].nusers++;
  
  release(&(drives->lock));
  
  return driven;
}

/* Safely decrements the user count of the given drive number, returning -1. */
int drives_close(struct drives* drives, int driven) {
  if (drives == NULL || driven < 0 || driven > DRIVES_MAX) {
    return -1; // Always returns -1 (whether driven is invalid or not)
  }
  acquire(&(drives->lock));
  drives->entries[driven].nusers--;
  release(&(drives->lock));
  return -1; // Always returns -1
}

/* Safely increments the user count of the given drive number, returning the number. */
int drives_dup(struct drives* drives, int driven) {
  if (driven < 0 || driven > DRIVES_MAX) {
    return -1; // Returns -1 if invalid
  }
  acquire(&(drives->lock));
  drives->entries[driven].nusers++;
  release(&(drives->lock));
  return driven;
}

fsinstance_t* drives_fsbegin(struct drives* drives, int hint, char* path) {
  int lench = drives_namelencheck(path);
  //printf("from path '%s' got lencheck %d\n", path, lench);
  //int nskip = lench < 0 ? 0 : lench+1;
  int dn = hint;
  acquire(&(drives->lock));
  if (lench >= 0) {
    dn = drives_find(drives, 0, path, lench);
    //printf("Found drive %d handler %d\n", dn, drives->entries[dn].handler);
  }
  if (dn < 0) {
    release(&(drives->lock));
    return 0ULL;
  }
  fsinstance_t* instance = drives->entries[dn].handlerdata;
  release(&drives->lock);
  fsinstance_begin(instance);
  return instance;
}

void drives_fsend(struct drives* drives, fsinstance_t* instance) {
  if (instance != NULL) {
    fsinstance_end(instance);
    // TODO: Add some more bookkeeping, i.e. begin/end should also imply an additional open/close of the relevant drive
  }
}

void* drives_fsnode(struct drives* drives, int hint, char* path, int* fstypevar) {
  int lench = drives_namelencheck(path);
  //printf("from path '%s' got lencheck %d\n", path, lench);
  int nskip = 0;
  if (lench >= 0) {
    if (path[lench+1] == '/') {
      nskip = lench + 1;
    } else {
      // Replace the ':' with a '/' to ensure we're in the drive's root
      path[lench] = '/';
      nskip = lench;
    }
  }
  int dn = hint;
  acquire(&(drives->lock));
  if (lench >= 0) {
    dn = drives_find(drives, 0, path, lench);
    //printf("Found drive %d handler %d\n", dn, drives->entries[dn].handler);
  }
  if (dn < 0) {
    release(&(drives->lock));
    return 0ULL;
  }
  if (fstypevar) {
    *fstypevar = drives->entries[dn].handler;
  }
  if (drives->entries[dn].handler != DRIVES_HANDLER_FS) {
    release(&(drives->lock));
    return 0ULL;
  }
  fsinstance_t* instance = drives->entries[dn].handlerdata;
  release(&(drives->lock));
  void* result = fsinstance_lookup(instance, path+nskip);
  return result;
}

void* drives_fsparent(struct drives* drives, int hint, char* path, int* fstypevar, char* namevar, int namelen) {
  if (namelen < FSFORMAT_NAMESIZE_NEW) {
    return NULL;
  }
  int lench = drives_namelencheck(path);
  //printf("from path '%s' got lencheck %d\n", path, lench);
  int nskip = 0;
  if (lench >= 0) {
    if (path[lench+1] == '/') {
      nskip = lench + 1;
    } else {
      // Replace the ':' with a '/' to ensure we're in the drive's root
      path[lench] = '/';
      nskip = lench;
    }
  }
  int dn = hint;
  acquire(&(drives->lock));
  if (lench >= 0) {
    dn = drives_find(drives, 0, path, lench);
    //printf("Found drive %d handler %d\n", dn, drives->entries[dn].handler);
  }
  if (dn < 0) {
    release(&(drives->lock));
    return NULL;
  }
  if (fstypevar) {
    *fstypevar = drives->entries[dn].handler;
  }
  if (drives->entries[dn].handler != DRIVES_HANDLER_FS) {
    release(&(drives->lock));
    return NULL;
  }
  fsinstance_t* instance = drives->entries[dn].handlerdata;
  release(&(drives->lock));
  void* result = fsinstance_lookupparent(instance, path+nskip, namevar);
  return result;
}

int drives_getinfo(struct drives* drives, int drivenumber, struct __syscdefs_driveinfo* structure) {
  if (!structure) {
    return -1;
  }
  
  // This will mark the drive as being opened but will also validate the
  // drive number first so we should use it's return value as the new
  // number as long as it's >= 0.
  int idx = drives_opensimple(drives, drivenumber);
  
  // The structure is cleared to zeroes before setting or returning,
  // even/especially in the case of the drive not existing!
  memset(structure, 0, sizeof(struct __syscdefs_driveinfo));
  
  // If the value returned by drives_opensimple is <0 then the drive
  // number doesn't exist or is out of range.
  if (idx < 0) {
    return -1;
  }
  
  if (drives->entries[idx].handler == DRIVES_HANDLER_FS) {
    fsinstance_t* instance = drives->entries[idx].handlerdata;
    memcpy(structure->name, drives->entries[idx].name, __SYSCDEFS_DRIVES_NAMEMAX);
    structure->drivenumber = idx;
    structure->blocksize = 4096; // TODO: Make this configurable!!!
    structure->totalblocks = instance->superblock->totalblocks;
    structure->freedatablocks = fsinstance_countfreeblocks(instance, instance->fslog_device);
    if (instance->fsversion == 0) {
      strcat(structure->fsname, "xv6-compatible (v0)");
    } else if (instance->fsversion == 1) {
      strcat(structure->fsname, "Herodotus FS v1");
    } else {
      strcat(structure->fsname, "Unrecognised version");
    }
  } else {
    return -1;
  }
  
  drives_close(drives, idx);
  
  return 0;
}